The invention relates to a method of demodulating binary data signals and has for its object to provide a method of demodulating a quadphase coded data signal, this data signal comprising words consisting of first, second, third and fourth equally long, consecutive half bit intervals.
The invention further relates to a receiver for carrying out the method.
Quadphase coding is known from the article by U. Appel and K. Trondle titled "Zusammenstellung und Gruppierung verschiedener Codes fur die Uebertragung digitaler Signale" which was published in the Nachrichten-technische Zeitschrift, Volume 1, 1970, pages 11-16, and FIG. 7 in particular. A quadphase coded signal is obtained by dividing the original binary data signal into groups of two bits, denoted dibits, and by placing the first and the second bits, respectively, of the dibit in the first and the second half bit interval, respectively, of the coded word, consisting of two bit intervals, and by placing the inverted value of the first and the second bit, respectively, of the dibit in the third and fourth half bit interval, respectively, of the coded word.
The coding method owes its name "quadphase" to the property that four basic signals can be distinguished, namely 0011, 1001, 0110 and 1100 (allotted to the dibits 00, 10, 01 and 11, respectively).